The present invention generally relates to annular seals, such as dynamic seals of the type used in turbomachinery. More particularly, this invention relates to a fixture and inspection method by which dimensional characteristics of an annular seal can be ascertained prior to installation.
Labyrinth-type packings and brush seals are widely used in steam turbines and in aircraft and industrial gas turbines to provide dynamic seals between rotating and static turbine components, such as the rotor and diaphragm inner web of a steam turbine. Traditional labyrinth packing comprises a series of teeth that project radially inward from the inner circumference of a static component and toward but out of contact with the adjacent rotary component, thereby defining a series of partial barriers that create a tortuous axial flow path immediately adjacent the surface of the rotary component. Brush seals comprise fibers or bristles that, similar to the teeth of a labyrinth packing, project radially inward from the inner circumference of a static component toward a rotary component. In contrast to labyrinth packings, brush seals are normally intended to be in rubbing contact with the adjacent circumferential surface of the rotary component, creating a substantially continuous barrier to flow around the circumference of the rotary component. In this regard, brush seals provide a more effective barrier to secondary flow losses, i.e., provide better sealing performance, as compared to labyrinth packings, and therefore have the potential for significantly improving section performance. However, because their sealing performance relies on rubbing contact, the conformance of a brush seal to its design dimensions and tolerances, particularly its internal diameter and concentricity, is important.
Brush seals have been developed that are manufactured as a full-annular structure and then cut to create multiple arcuate segments that can be later reassembled during installation to reestablish the original annular seal structure. In a particular example, a brush seal formed of high strength polymer (e.g., KEVLAR®) is sectioned along its diameter to create two semicircular (180-degree) arcuate segments. The flexible nature of the polymeric material along with residual stresses (in the back structure supporting the bristles) that are redistributed during cutting causes each segment to have altered inner diameter (ID) dimensions. As a result, dimensional inspection of the seal in its “free” (uninstalled) state is difficult and leads to an increased risk of seals that do not conform with design dimensions and tolerances. Though the seal can be inspected after its segments are reassembled during final installation, such an approach can be impractical because of the limited space of typical turbine installations and the difficulty with which such an inspection can be performed in the field.
In view of the above, it would be desirable to verify the dimensional characteristics of a segmented brush seal (as well as other annular seals) without the requirement to install the seal prior to inspection.